US Open 2018: Roger Federer Defeated by Australian John Millman

Roger Federer served poorly. He volleyed poorly. Closed out sets poorly, too. And now he's gone, beaten at the U.S. Open by an opponent ranked outside the top 50 for the first time in his illustrious career. (Image: AP)

Looking slow and tired on a sweltering night in Arthur Ashe Stadium, the No. 2-seeded Federer double-faulted 10 times, failed to convert a trio of set points and lost 3-6, 7-5, 7-6 (7), 7-6 (3) in the fourth round to John Millman in a match that began Monday (September 03) and concluded at nearly 1 am on Tuesday (September 04). (Image: AP)

To Federer, it was all about the heat and the humidity. With the temperature in the 80s, even with the sun down, and the humidity at about 75 percent, he was unable to summon his usual verve. (Image: AP)

"Was just one of those nights where, I guess, I felt I couldn't get air. There was no circulation at all. I don't know, for some reason I just struggled in the conditions tonight. It's one of the first times it's happened to me," the 37-year-old Federer said. (Image: AP)

"It's uncomfortable. Clearly just keep on sweating more and more and more and more as the match goes on. You lose energy as it goes by. But John was able to deal with it better," Federer added. (Image: AP)

Millman was adamant he would not be intimidated by Federer, and perhaps was helped by having spent time practicing together a few months ago ahead of the grass-court portion of this season. (Image: AP)